That’s all well and good, Marty, but stop squirming and tell us how much you’d price carbon at? That’s all we really care about:

Weitzman hemmed and hawed and noted that the whole point of his paper was that there are these big uncertainties, and that previous attempts to calculate the socially optimal price on carbon haven’t accounted for these and thus are wrong, and that you couldn’t even really do the calculation with the current tools we have. But he finally acknowledged that if you made him philosopher-king and demanded an answer he would say that the price on emissions (i.e. a carbon tax or the price of a cap-and-trade permit) should be $50 per ton of CO₂, rising at rate of a few percent over inflation.